Nitrogen-retaining property of compost in an aerobic thermophilic composting reactor for the sanitary disposal of human feces

Aerobic composting is a method for the sanitary disposal of human feces as is used in bio-toilet systems.As the products of composting can be utilized as a fertilizer,it would be beneficial if the composting conditions could be more precisely controlled for the retention of fecal nitrogen as long as possible in the compost.In this study,batch experiments were conducted using a closed aerobic thermophilic composting reactor with sawdust as the bulk matrix to simulate the condition of a bio-toilet for the sanitary disposal of human feces.Attention was paid to the characteristics of nitrogen transformation.Under the controlled conditions of temperature at 60°C,moisture content at 60%,and a continuous air supply,more than 70%fecal organic removal was obtained,while merely 17%fecal nitrogen loss was observed over a two-week composting period.The nitrogen loss was found to occur mainly in the first 24 h with the rapid depletion of inorganic nitrogen but with an almost unchanged organic nitrogen content.The fecal NH4-N which was the main component of the inorganic nitrogen(>90%)decreased rapidly in the first day,decreased at a slower rate over the following days,and finally disappeared entirely.The depletion of NH4-N was accompanied by the accumulation of NH3 gas in the ammonia absorber connected to the reactor.A mass balance between the exhausted NH3 gas and the fecal NH4-N content in the first 24 hours indicated that the conversion of ammonium into gaseous ammonia was the main reason for nitrogen loss.Thermophilic composting could be considered as a way to keep a high organic nitrogen content in the compost for better utilization as a fertilizer.

Empirical analysis of mass flow and operation performance of a full-scale biogas plant for human feces treatment

With the rapid development of urbanization in China,the existing municipal network cannot cover all areas and solve all human waste treatment problems.Biogas plants,as an important nationally developmental strategy for cleaner energy production and environmental protection,have been widely used in many industrial and agricultural fields.This research analyzed the mass flow and operation performance in a biogas plant treating human feces at a practical rather than laboratory scale.The biogas plant operated on mesophilic semi-continuous mode at the organic loading rates(OLRs)of 0.56 kg volatile solid(VS)/(m³·d)and average total solid(TS)contents of 3.50%.Results showed that the average biogas production and methane yield were(145±10)m³/d and(471±17)m³CH4/(t VS),respectively.Annual total feeding amount was 2555.0 t.Among these,there were 58.04 t biogas and 2496.97 t digestate,including 43.07 t solid residues and 2453.90 t liquid digestate.For the full-scale biogas plant,anaerobic bacteria could acclimatize to high total ammonia nitrogen(TAN)concentration(3659 mg/L)and tolerate high free ammonia nitrogen(FAN)concentration of 561 mg/L.It also had strong autoregulation for adapting the large range(2.02-15.18 g/L)and high concentration(15.18 g/L)of influent volatile fatty acid(VFA).In order to achieve its sustainable development and high efficient operation,it is very important to improve the feeding concentration,using digestate to dilute raw material and adding some high C/N raw material in human feces.In conclusion,the biogas plant was an excellent alternative technology for treating human feces.

An Improved Methodology to Overcome Key Issues in Human Fecal Metagenomic DNA Extraction

Microbes are ubiquitously distributed in nature, and recent culture-independent studies have highlighted the significance of gut microbiota in human health and disease. Fecal DNA is the primary source for the majority of human gut microbiome studies. However, further improvement is needed to obtain fecal metagenomic DNA with sufficient amount and good quality but low host genomic DNA contamination. In the current study, we demonstrate a quick, robust, unbiased, and cost-effective method for the isolation of high molecular weight （〉 23 kb） metagenomic DNA （260/280 ratio 〉 1.8） with a good yield （55.8 ± 3.8 ng/mg of feces）. We also confirm that there is very low human genomic DNA contamination （eubacterial： human genomic DNA marker genes = 227.9：1） in the human feces. The newly-developed method robustly performs for fresh as well as stored fecal samples as demonstrated by 16S rRNA gene sequencing using 454 FLX＋. Moreover, 16S rRNA gene analysis indicated that compared to other DNA extraction methods tested, the fecal metagenomic DNA isolated with current methodology retains species richness and does not show microbial diversity biases, which is further confirmed by qPCR with a known quantity of spike-in genomes. Overall, our data highlight a protocol with a balance between quality, amount, user-friendliness, and cost effectiveness for its suitability toward usage for cultureindependent analysis of the human gut microbiome, which provides a robust solution to overcome key issues associated with fecal metagenomic DNA isolation in human gut microbiome studies.

Spatial distribution of bacterial resistance towards antibiotics of rural sanitation system in China and its potential link with diseases incidence

Chinese government is vigorously promoting toilet renovation in rural areas to reduce the risk of human feces exposure,which would cause infectious diseases,especially antibiotic resistance genes(ARGs)and pathogens.However,the distribution of ARGs in human feces from different regions of China remained ill-defined.It is not yet known how the survival of ARGs after toilet treatment is associated with the regional infection rates.Here,we investigated the prevalence of ARGs in human feces in rural areas of China and their potential relationship with infectious diseases for the first large-scale.The results showed that there were still high ARGs residues in human feces after rural toilet treatment,especially tetM-01 and ermB with average relative abundance as high as 1.21×10^(−1)(Eastern)and 1.56×10^(−1)(Northern),respectively.At a large regional scale,the significant differences in human feces resistomeswere mainly shaped by the toilet types,TN,NH_(3)-N,and the bacterial community.A critical finding was that toilets still cannot effectively decrease the pathogenicity risk in human feces.The significant positive relationship(P<0.05)between infectious diseases and ARGs can infer that ARGs in human feces exposure might be a critical path for enhancing the incidence of diseases,as these ARGs hinder the effectiveness of antibiotics.